Slightly off-topic, but I have looked through my FatJoe.co posts. I wanted to see whether they were on real sites or not.
I've ordered over 50 posts from them, mainly on higher DA (20+ or 30+) sites.
1 low DA site no longer exists. 5 posts have been taken down by the site owners. 1 seems to be a PBN site.
The other sites probably would pass a manual review, but 17 of them seem to exist for the sake of selling guest posts. They aren't quality sites, despite the high DA metric. But as we know, DA can be manipulated easily.
They seem to deliver what they say they deliver. I personally doubt the effectiveness of these posts simply because the blogs have such high OBL. Some of the posts have 5 links on them, before footers and sidebars are considered.
I'd use a few to establish niche relevancy and perhaps help with anchor text profile, but they aren't going to move mountains.